1. Field of the Invention
The present invention generally relates to an information recording apparatus, and more particularly to an information recording apparatus for recording information on an additionally writable recording medium such as a write once (WO) type optical disc on which information can be written only once at the same location or on a rewritable (RW) optical disc on which information can be rewritten any number of times at the same location.
2. Description of Related Art
In an information recording apparatus of the type mentioned above, when information data is written on an additionally writable recording medium, a writing clock signal is generated for writing the information data on the disc while establishing synchronization with the information data to be written. Stated another way, the information data is generally written on the disc in synchronism with the generated writing clock signal having a stable predetermined frequency (for example, so-called bit synchronization is established). The writing clock signal is typically generated from a reference clock generator, for example, a quartz oscillator or the like which can provide an oscillation output by itself.
However, when a write-once or additional write operation is performed on a disc, which has information data partially written thereon, for writing new information data subsequent to the written information data, a writing clock signal used for the written information data may differ in phase from a writing clock signal used for the new information data.
In this event, in an operation for reading the resulting disc after recording the new information data to sequentially reproduce the old and new information data, it is often difficult to reproduce clock signals for synchronizing the data read from the disc near the junction of the old and new information data.
Particularly, when information data is subsequently written on a disc on which information data has been written by an information recording apparatus using a different information recording apparatus, different writing clock signals are generated at respective recording times from different clock sources, even if these information recording apparatus belong to the same type, whereby preceding information data and subsequent information data are inevitably written with different writing clock signals having different frequencies as well as different phases.
Reproduction of a clock signal for synchronizing read data involves the use of a PLL (Phase Locked Loop) circuit which is supplied with the read data as an input. A disc having recorded thereon preceding and subsequent information data with writing clock signals largely different in phase and frequency from each other will significantly disturb the synchronization operation of the PLL circuit near the junction of the preceding data and the subsequent data. As a result, a decoder for decoding read data based on the clock signal for synchronizing read data may erroneously detect a variety of data in the read data.
Also, data is written on a disc in a format which includes a particular synchronization signal for each data block for carrying a predetermined amount of information in addition to the bit synchronization as mentioned above, such that an associated data block is synchronized during reproduction. Even such a particular synchronization signal is located in data based on the writing clock signal. Therefore, the writing clock signals largely different in phase and frequency from each other, generated as mentioned above, will cause the interval between a particular synchronization signal located at the end of the preceding information data and a particular synchronization signal located at the beginning of the subsequent information data to be largely different from intervals before and after that interval, possibly resulting in the inability of detecting the particular synchronization signal and erroneous detection during reproduction. Particularly, this would be a grave problem for a player having poor performance of detecting such a particular synchronization signal.
Thus, the present invention has been made in view of the problem mentioned above, and its object is to provide an information recording apparatus which is capable of employing a recording form for a recording medium which permits written data and additional data written subsequent thereto to be smoothly reproduced in sequence without disturbing a synchronization operation for read data upon reproduction of information.
To achieve the above object, the present invention provides an information recording apparatus capable of additionally recording new data subsequent to previously written data on a recording medium, which comprises writing clock generating means for generating a writing clock signal for writing the new data into the recording medium while establishing synchronization with the new data, clock reproducing means for reading the written data from the recording medium, and reproducing a synchronization clock signal of the written data to generate a reproduced clock signal, and phase adjusting means for synchronizing the phase of the writing clock signal to the phase of the reproduced clock signal.
In the information recording apparatus mentioned above, the written data is data including a particular synchronization signal for every predetermined data block. The information recording apparatus may be configured to further comprise synchronization signal detecting means for detecting the particular synchronization signal from the written data, counting means responsive to detection timing of the particular synchronization signal by the synchronization signal detecting means to start a counting operation based on the reproduced clock signal, and control means for determining a writing start time at which the new data is written into the recording medium, based on a count value presented by the counting means.
In the information recording apparatus mentioned above, the phase adjusting means may synchronize the phase of the writing clock to the phase of a reproduced clock signal derived from the written data in a predetermined period before an additional recording start position for the new data on the recording medium.
Further, in the information recording apparatus mentioned above, the phase adjusting means, after synchronizing the phase of the writing clock signal to the phase of the reproduced clock signal, may be configured to return the writing clock signal to a frequency and a phase inherent to the writing clock generating means with a predetermined time constant.
The present invention also provides an information recording apparatus capable of additionally recording new data subsequent to previously written data on a recording medium, which comprises comparing means for comparing, in terms of value, an end data portion corresponding to a predetermined amount of data located at the end of the written data with a top data portion corresponding to the predetermined amount of data located at the beginning of the new data, and control means for changing values in the new data when the comparing means determines that values in the end data portion are coincident with values in the top data portion.